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Topic: 16.4 volts at the battery (Read 5486 times)

I'd be looking at the Blue wire to the voltage regulator that I think is the same power that is supplied for the ignition.As I understand it that is what the VR monitors to see if the battery needs more or less charging (should be same as battery voltage) so if it's not connected well the VR is fooled into thinking it should make the alternator send more juice. RE: the ground cable, I'd think if it were a problem cranking the car would be an issue.

Yeah that blue wire is the one that also feeds the choke and a couple other things.....and connects to the one field connector on the alternator.....thats the one reading 14.8 volts and I cant see any issues with it....

It's loosing a volt somewhere ... recently saw a post that someone had a Ammeter that had high resistance, also this power runs trough the steering column harness & plug which is a week link.

Do you have a ground strap from the motor to the firewall?... don't know if not having one would cause this but the factory put one there for a reason..

I have a ground strap from the fireall/ecu to the motor (valve cover bolt) and one from the firewall/VR to the same bolt. I ran a separate temporary jumper wire from the VR/firewall to the battery negative and no change.

My ammeter has been bypassed (one of the first things I did years ago).

I'd be looking at the Blue wire to the voltage regulator that I think is the same power that is supplied for the ignition.As I understand it that is what the VR monitors to see if the battery needs more or less charging (should be same as battery voltage) so if it's not connected well the VR is fooled into thinking it should make the alternator send more juice. RE: the ground cable, I'd think if it were a problem cranking the car would be an issue.

The blue wire is where the regulator senses system voltage and when functioning properly, will try to field the alternator to maintain (regulate) 14 volts +- .2 volts. Raise the idle when testing the alternator to 1200-1500 rpm. The amperage output at idle too low to test properly, especially a roudback alternator. Based on the testing that you have done already, it appears that your voltage regulator and alternator are working, but there is a voltage drop on the blue wire feeding power to the regulator, throwing the alternator output voltage out of range. Do you have a hand held digital voltmeter for testing?

The blue wire is where the regulator senses system voltage and when functioning properly, will try to field the alternator to maintain (regulate) 14 volts +- .2 volts. ......<snip>......but there is a voltage drop on the blue wire feeding power to the regulator, throwing the alternator output voltage out of range. Do you have a hand held digital voltmeter for testing?

Yes I have a meter...

But HOW do I test it? What am I looking for?

I had previously tested the blue/purple wire at the VR and it was lower in voltage....but should I be testing that when connected to the VR or disconnected? With engine running or not?

I had previously tested the blue/purple wire at the VR and it was lower in voltage....but should I be testing that when connected to the VR or disconnected? With engine running or not?

All the connectors seem ok...choke connector, ballast connector, etc

First thing is I'm sorry you have been dealing with this overcharging issue for so long! I'll explain how to test your charging system for you. 40+ years as a service professional, I do this on a daily basis. You are looking to locate the source of the voltage drop (resistance) in the charging system. We will test the charging system running and loaded, VR connected with the engine rpm set at 1200-1500 rpm for accuracy. To start off; In a perfect world there will be no difference between the battery positive terminal voltage and the voltage reading at the blue wire (at the VR).On the ground side, the VR attaching ground screw, and battery negative terminal. The alternator positive output terminal and the battery + terminal and last the alternator case ground and the battery negative terminal. Does this make sense?

So I should use the pin method and see what the vr is seeing when plugged in? Or disconnect and check?

Ok when your ready we can start at the beginning. Completely reconnect the charging system so it's ready to go, then start the engine and set the idle to 1200-1500 rpm. Turn on all the accessories in the car, headlights on high beam, interior light etc. Leave the flashers/blinker off. We want a constant load. Now take these readings:

A- Battery voltage. Positive test lead on the positive battery POST (not the battery wire terminal). Negative test lead to the negative battery POST (not the wire terminal. Write down the voltage reading as A.

B- Alternator output ground side voltage drop: Connect the negative test lead to a clean bare metal spot on the alternator housing. Connect the positive test lead to the Negative battery post, (not the battery wire terminal). Write down the reading as B.

C- Alternator output positive side voltage drop: Connect the positive test lead to the output (+) terminal on the alternator, attach the negative test lead to the battery Positive Post. Write down this reading as C.

Ok when your ready we can start at the beginning. Completely reconnect the charging system so it's ready to go, then start the engine and set the idle to 1200-1500 rpm. Turn on all the accessories in the car, headlights on high beam, interior light etc. Leave the flashers/blinker off. We want a constant load. Now take these readings:

A- Battery voltage. Positive test lead on the positive battery POST (not the battery wire terminal). Negative test lead to the negative battery POST (not the wire terminal. Write down the voltage reading as A.

B- Alternator output ground side voltage drop: Connect the negative test lead to a clean bare metal spot on the alternator housing. Connect the positive test lead to the Negative battery post, (not the battery wire terminal). Write down the reading as B.

C- Alternator output positive side voltage drop: Connect the positive test lead to the output (+) terminal on the alternator, attach the negative test lead to the battery Positive Post. Write down this reading as C.

Others may wonder about the procedure listed by 734406pk, but they are right on.. it's measuring the voltage 'drop' from end to end of each circuit... all wiring and connections provide a resistance to current flow.. the more resistance in the circuit, the more drop there will be from one end to the other... by using low voltage scale on meter, you can read what the difference in voltage is from one end of the circuit to the other... the higher the voltage reading end-to-end, the more resistance there is in that circuit... the worse the voltage drop is... BAD

Ideally, you want ZERO volt readings (no resistance end to end) on the circuits described, but there will always be some resistance in the wires/connections.

Others may wonder about the procedure listed by 734406pk, but they are right on.. it's measuring the voltage 'drop' from end to end of each circuit... all wiring and connections provide a resistance to current flow.. the more resistance in the circuit, the more drop there will be from one end to the other... by using low voltage scale on meter, you can read what the difference in voltage is from one end of the circuit to the other... the higher the voltage reading end-to-end, the more resistance there is in that circuit... the worse the voltage drop is... BAD

Ideally, you want ZERO volt readings (no resistance end to end) on the circuits described, but there will always be some resistance in the wires/connections.

Thank You! This method for testing voltage drop may be a little tough to understand at first (it was for me!) but its incredibly accurate. The plan is to test the entire charging system this way.

The only thing I would add to this is that IF you get a large voltage drop when reading to either of the battery posts, the first thing to check is the battery cable to battery post connections...

they always seem to 'corrode' first, and ground post faster than positive post... (it will build up an oxidized layer between the inside connector surfaces and post surfaces). Use a battery terminal cleaner/wire brush to remove the corrosion, and apply some dielectric grease to the connectors when re-attaching them, to help prevent buildup in the future.